1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive element in which an inner electrode layer is not easily worn and which has an excellent lubricant circulating or cooling property.
2. Description of the Related Art
To prevent global warming which is one of global environment problems, there has been developed a technology for reducing a fuel consumption of a car. As an environment-friendly power source of the car, a fuel cell is considered to be prevailing, but there are many technical and economical problems in realizing this power source. To solve the problems, a hybrid engine system used together with an electric motor is put to practical use. In addition, especially in Europe, there largely increases market share of a car having an improved diesel engine mounted thereon, in which emissions of deleterious substances have been reduced.
The diesel engine is an engine in which a fuel is injected to a cylinder and compressed at a high pressure to be self-ignited. Moreover, an engine output is controlled by a fuel injection amount. Therefore, in the diesel engine, a role of a fuel injecting device is important which feeds a fuel into the cylinder. In recent years, a reason why the diesel engine is increasingly used mainly lies in development of a so-called common rail type fuel injecting device. Especially, from now on, it is expected that adopting of a piezoelectric element instead of a solenoid promotes spreading of use of the diesel engine. Since the piezoelectric element can realize opening and closing of an injection nozzle at a higher speed as compared with the solenoid, it is possible to feed a more appropriate amount of fuel to the cylinder. An optimum combustion condition of the fuel can be formed. As a result, excellent effects are brought about: reduction of deleterious substances such as particulates, nitrogen oxide, carbon monoxide and hydrocarbon included in an exhaust gas; reduction of the fuel consumption; reduction of an engine noise; and improvement of an engine output.
The piezoelectric element to be applied to the fuel injecting device is utilized as a driving source of an injection nozzle opening and closing mechanism which generates a displacement or a stress. The element contained in a metal casing or the like is used in many cases. The piezoelectric element of a laminated type is usually applied. In general, this laminated piezoelectric element is prepared by: laminating the predetermined number of piezoelectric tapes in which patterns of a conductive material constituting an inner electrode are formed, and dividing this laminated green article into individual elements by processing such as cutting; or dividing a sintered block obtained by firing into individual elements by processing such as cutting. Therefore, the piezoelectric element has an outer flat surface formed by the processing. It is to be noted that as a prior document, JP-A-2001-339105 is cited.
Such conventional laminated piezoelectric element is contained in the casing as described above, and an expanding and contracting operation is performed in the casing. Therefore, an outer surface (side surface) of the piezoelectric element is slid. Therefore, needless to say, an end portion of the inner electrode exposed on the outer surface (side surface) of the piezoelectric element is ground by a friction with an inner surface of the casing. Thus, there has been a problem in reliability of a long-term operation. On the other hand, for a purpose of lubrication to inhibit such wearing phenomenon or a purpose of shutting out humidity of outside air, the piezoelectric element is sometimes contained together with the lubricant in the casing, and used. However, since the side surface of the piezoelectric element is flat, there is uncertainty around the lubricant or in cooling the lubricant and resultantly cooling the piezoelectric element. Therefore, the improvement of the reliability of the element has been required.